<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      .box {
        width: 100px;
        height: 100px;
        background: red;
      }
      .active {
        color: white;
      }
    </style>
  </head>
  <body>
    <div class="box">hello</div>
    <button>点击1</button>
    <button>点击2</button>
    <script>
      // var ele = document.querySelector(".box");
      // ele.onclick = function(){
      //     this.className += " active";
      // }

      // 操作类名  classList 对象 来操作类名；
      var ele = document.querySelector(".box");
      // 1.添加类名 classList.add("类名");
      ele.onclick = function () {
        this.classList.add("active");
      };
      // 2.移除某个类名；classList.remove("类名");
      //     var str = "box active";
      //   var res =   str.replace(" active","");
      //   console.log(res);
      var btns = document.querySelectorAll("button");
      btns[0].onclick = function () {
        ele.classList.remove("active");
      };

      // 3.判断元素是否包含某个类名；classList.contains
      btns[1].onclick = function () {
        var res = ele.classList.contains("active");
        console.log(res);
      };
    </script>
  </body>
</html>
